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PaulDotCom Security Weekly is a weekly podcast hosted by a group of network penetration testers and SANS instructors that covers some of the tactics and tools that attackers use as well as news and information for how sysadmins can protect their systems.

Mind of Root is a weekly podcast that covers more of the general sysadmin topics.

Radio Free Security is a monthly podcast from WatchGuard (they make security appliances). They have a lot of good insight on security and protecting your network.

http://itpodcast.org/blog/about/ -
This site was started on January 2nd,
2008 with the intention to house a
blog and post podcasts I intend to
produce surrounding healthcare IT and
the issues we are working through in
this business. I hope that others will
find this useful, and that this will
become a resource others in our
industry will use.

Hak5 bills itself as a TV show about hacking. They cover a lot of weird stuff like installing linux on gameboys, but at the end of the day they do a lot of hands-on tutorials with networking software and server hardware. The sysadmin-relevant parts of the show are a bit Windows heavy sometimes but they also have lots of Linux coverage and use it often in their projects.